I. Field of the Invention
The present invention relates to millimeter wave device structures and methods of making. More specifically, the present invention relates to a novel and improved millimeter wave device featuring a sandwich-type construction and methods of accurate, high throughput manufacture.
II. Background Art
Current state-of-the-art millimeter wave devices for operating at frequencies employing signals having a wavelength of one to ten millimeters are traditionally constructed in metal waveguide. Typical construction techniques implement the traditional dimensional milling of the metal structure. However, since the waveguide dimensions are proportional to the operating wavelength, these dimensions become smaller as the frequency increases. As the frequency of the device increases, the complexities of traditional fabrication and the strict tolerances required become extremely difficult to achieve. In large quantity production schemes, traditional precision milling techniques are extremely cost prohibitive in achieving the precision required for devices in all types of applications.
In an attempt to solve problems of yield, size and weight associated with millimeter wave device structures which are required to provide perform at frequencies in excess of 100 GHz, several alternate methods of constructing transmission lines and circuits have been employed.
Millimeter wave devices are typically manufactured in microstrip, coplanar waveguide and slot line structures. However, millimeter wave devices manufactured as microstrip, coplanar waveguide and slot line structures are not practical due to the high losses encountered at frequencies above 60 GHz.
Another approach in fabricating millimeter wave devices is constructing the device in a dielectric image guide structure. However, intolerable levels of radiation and scattering are generated in the dielectric image guide structures. The undesirable effects in these structures are the result of discontinuities caused by devices such as ferrites and diodes contacting the dielectric lines. Of these structures, microstrip, coplanar waveguide, slot line and dielectric image guide, none offer the high performance required in millimeter wave devices which operate at frequencies in excess of 100 GHz.
Alternate structures for millimeter wave devices have utilized finline or suspended strip line. In these types of structures, transmission lines and mixers have shown good performance at the higher millimeter wave frequencies. However, other components manufactured in these structures have had less than successful performance. The limitations upon finline and suspended strip line structures are a result of prevent construction techniques. These techniques require high precision machining of air channels along with critical positioning of the substrate and ground surfaces. The requirement of high precision machining pose significant problems in large quantity manufacturing, especially on a cost-effective basis.
Overall, in the area of millimeter wave devices operating at frequencies in excess of 70 GHz, little activity in developing accurate devices adaptable to a low cost, high volume production process has been undertaken. A major reason for lack of activity in this area is due to the complexity of fabrication of these high frequency devices. The implementation of the usual fabrication techniques for millimeter wave devices typically results in poor electrical high frequency performance. Implementation of standard manufacturing techniques in the manufacture of millimeter wave devices, which is only hoped to achieve satisfactory operating characteristics, has projected production costs which are highly excessive in high quantity production runs. Therefore, millimeter wave device usage in large scale programs has been quite limited mainly due to technical difficulties, cost prohibitions of large quantity production, and lack of reproduction accuracy in unit performance.
It is therefore, an object of the present invention to provide a novel and improved high performance millimeter wave device and method of manufacture.
It is yet another object of the invention to provide a method for fabricating high performance millimeter wave integrated circuit devices utilizing high volume fabrication techniques.